Bathurst Burr

Common and Scientific Names

Bathurst burr

Xanthium spinosum

Origin and Distribution

Bathurst burr originated in South America (probably Argentina) and is now a cosmopolitan weed in warm temperate and semi-arid regions of the world. It was introduced to Australia in the 19th Century and has been declared a noxious weed in Victoria. Bathurst burr is found throughout most of Victoria but is most prevalent in the northern districts.

Description

Figure 1. Bathurst burr.

An erect, much branched, herb growing mainly in summer, it commonly grows 30 to 60 cm high, occasionally to 1 m, reproducing by seed. Most germination occurs after rain or irrigation in late spring and summer. Older plants produce burrs in February while late germinating plants produce them when only a few weeks old. Plants generally die early in winter but mature plants may be found at any time of year.

Stems - Greenish yellow with fine short hairs, armed at the base of each leaf and stem node with one or two triple-pronged yellow spines which are 1.5 to 2.5 cm long.

Leaves - up to 7 cm long, alternate and divided into three lobes; dark green and shiny above with prominent pale veins, downy and pale green or whitish beneath.

Flowers - creamy green, small and inconspicuous, wind pollinated, appearing from February to July. Female flowers occur beneath the leaf axils; male flowers at the ends of stems.

Fruit - an ovoid, straw-coloured, hairy burr, 1 to 1.5 cm long and 4 to 5 mm wide, covered with many yellow-orange hooked spines and sometimes with one or two straight terminal beaks. When ripe the burr is hard and woody. Other species of Xanthium found in Australia have burrs which are considerably larger.

Seeds - flat, brown or black, 1 cm long, two in each burr. Seed may remain dormant in the soil for three years.

The Problem

Bathurst burr is common in pastures (particularly around stock yards and watering points) and infestations occur frequently along water courses. It is rarely grazed by livestock because of the long spines. The burrs are one of the most common contaminants of wool. They become entangled in the neckline and belly wool, requiring severe skirting and devalue the product. Burrs also cause irritation to shearers and damage shearing equipment. Spines on the burrs damage the feet of sheep and other animals.

Bathurst burr is a prevalent weed of summer crops such as grapes, tomatoes and sunflowers where it can form dense stands, and may interfere with manual harvesting operations. It can also act as a host for a number of fungal pathogens found in horticulture, and causes contact dermatitis in some people.

Hydroquinone is present in the seed and persists in the young plants, making the seedlings toxic to sheep, goats, cattle, horses, pigs and poultry. Poisoning may result in nausea, vomiting, depression and death, but is not a major problem in Australia.

Dispersal

The burrs attach to the coats of animals and to other fibrous material by their hooked spines. Dispersal in the fleece of sheep is common. The fruits float and are readily dispersed in water. Seed harvested from summer crops is sometimes contaminated with weeds such as Bathurst burr, which may be spread in this way.

Other management techniques

Changes in land use practices and spread prevention may also support Bathurst burr management after implementing the prescribed measures above.

Biological Control

An indigenous Australian blight fungus (Colletotrichum orbiculare) occurs on some infestations and is being developed by New South Wales Agriculture as a mycoherbicide. The accidentally introduced rust fungus, (Puccinia xanthii) affects both Noogoora burr and Bathurst burr. The Bathurst burr seed fly (Eurraresta bullans) was introduced from South America in the 1920s and affects large areas of burr in NSW and Queensland but provides no long-term control.

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